Tachycardia is a heart condition defined in an adult as a heart rate faster than 100 beats/minute. Tachycardia can broadly be classified as either sinus tachycardia, supraventricular tachycardia, or ventricular tachycardia. Sinus tachycardia is generally caused by exercise or emotional stress and is usually non-pathological. Supraventricular tachycardia is defined as a tachycardia that originates above the bifurcation of the bundle of His. Supraventricular tachycardia generally does not result in significant decreases in cardiac output. Ventricular tachycardia is defined as a tachycardia that originates below the bifurcation of the bundle of His. Ventricular tachycardia can result in profound decreases in cardiac output.
Discrimination between the various types of tachycardia is important to the effective management of patients with heart conditions. This is because some instances of tachycardia can be quite normal and would not warrant therapeutic intervention, while others can have serious consequences including chest pain, syncope, and death. One way of assessing the seriousness of a tachycardia is by evaluating its effect on cardiac output. Tachycardia that leads to insufficient cardiac output can be referred to as hemodynamically unstable tachycardia. In contrast, tachycardia where cardiac output remains sufficient to sustain life can be referred to as hemodynamically stable tachycardia.
Implantable medical devices are used to treat patients with various conditions of the heart including tachycardia. In some cases, an implantable device is used to deliver a high-energy shock to a patient's heart to terminate a tachycardia. High-energy shocks are generally successful at terminating tachycardia. However, such shocks cause extreme discomfort for patients. In addition, such shocks also use a substantial amount of energy and thus shorten the battery life of the device.
Many types of cardiac rhythm management (CRM) devices are capable of detecting abnormalities of heart rhythm through the analysis of myocardial electrical activity. However, it remains difficult to discriminate between different types of tachycardia using only myocardial electrical activity.
For at least these reasons, a need remains for systems and methods of discriminating between different types of tachycardia.